Ninth International Conference on Permafrost ... - IARC Research

Modeled Continual Surface Water Storage Change of the Yukon River BasinRena BryanLarry D. HinzmanRobert C. Busey<strong>International</strong> Arctic Research Center, University of Alaska Fairbanks, Fairbanks, Alaska, USAIntroductionClimate change in high latitudes, occurring at an observablepace, provides a window into changes the rest of the earthmay experience over a longer time scale (Shaver et al. 1992).Large-scale datasets of surface water, groundwater, andpermafrost dynamics serve as prerequisites in a variety ofother analyses and applications (Lehner et al. 2008). Thisstudy models continual surface water storage change inthe Yukon River Basin. The project is the underpinning forcarbon dioxide and methane flux; taiga-tundra shift; regionalsurface energy balance; regional weather pattern; migratorywaterfowl habitat availability; and infrastructure, building,and community stability studies.The purpose of this study is to determine how the futuresurface water storage of the Yukon Basin will compareto present. The project considers the changes to surfacewater storage as affected by warming climate, permafrostdegradation, and the vertical flux of water, but ignoreschanges induced by altered evapotranspiration or lateralflow. Transition from birch forests to fens and bogs hasbeen documented over the last twenty years in the TananaFlats (Jorgenson et. al. 2001). Also in the last twenty years,thermokarst lakes developed and initiated large taliks thatcompletely penetrated the permafrost near Council, Alaska.As a result, drier environments than before exist near Council(Yoshikawa & Hinzman 2003). In areas of discontinuouspermafrost, where projected permafrost will be warmenough to degrade, (1) if the local hydraulic gradient isupwards, the surface will be inundated with water and (2)if the hydraulic gradient is downwards, existing surfacewater will drain. In areas of continuous permafrost, whereprojected permafrost will be warm enough to degrade, thesurface will subside and surface ponds may increase. Toinvestigate this hypothesis, we utilize synoptic meteorology,permafrost thermal composition, and potentiometric surfacealgorithms.BackgroundAccording to the <strong>International</strong> Permafrost AssociationCircum-Arctic Map of Permafrost and Ground-IceConditions (Brown et al. 1998), discontinuous permafrostdominates the interior of the basin. Continuous permafrost issecond most prominent and present in the northern rim of thebasin and at Yukon-Kuskokwim Delta. Sporadic permafrostexists in southern Yukon Territory. Isolated permafrostcan be found sparsely in the glaciated region at the river’ssource. Closer examination of local variation in vegetation,soil moisture and thermal properties, and snow coverproduces finer resolution permafrost thermal composition(Smith & Riseborogh 1996). Continuous permafrost, frozenground (0°C and below) in spatial continuity, provides animpervious barrier to groundwater movement. Because ofoverall permafrost stability, much of the Arctic is spottedby ponds perched above the permafrost. Most groundwatersurfacewater interactions occur in areas of discontinuouspermafrost. In areas where the hydraulic gradient isdownwards, as the confining layer of permafrost degradesand an open talik forms, surface water formerly underlainby permafrost can drain into the subpermafrost groundwater.In contrast, where the local hydraulic gradient is upwards,subpermafrost groundwater may discharge at the surface.MethodsReferencing topographic features, the weather forecastmodel, National Weather Service Global Forecast System,is synoptically represented and accounts for topographicallydriven processes. TopoClimate is developed at the <strong>International</strong>Arctic Research Center, University of Alaska Fairbanks byAtkinson and Gourand. Driven by high-resolution surface airtemperatures available from TopoClimate, the TTOP modelis a numerical model using surface n-factors, bulk thermalconductivities, and freezing and thawing indices. TTOPwas originally developed by Smith & Riseborough (1996)(Busey et al. 2008). The model is applied to estimatingthe permafrost thermal composition in the Yukon Basin.Extracting steepness and relative elevations from the digitalelevation model, modeled potentiometric surfaces generate ahydraulic gradient map. (1) The surface air temperature, (2)permafrost thermal composition, and (3) hydraulic gradientmaps in concert assess surface water storage change. Thisstudy reviews existing observations of spring, aufeis, and lakesize and distribution change locations in order to calibrate themodel. Remote sensed imagery analysis has defined someareas of lake change. Thermal conductivity, thermokarst,and δ 18 O field observations validate the model. Thermalconductivity measurements and thermokarst documentationvalidate permafrost thermal composition modeled by TTOPand permafrost destabilization. The δ 18 O values from lakeswith a deep groundwater component are distinct from thoselacking connection to the groundwater. Lakes possessing adeep groundwater component as revealed by isotope analysisvalidate the hydraulic gradient model. Model validation datawill be collected in Innoko National Wildlife Refuge, YukonFlats National Wildlife Refuge, and locations throughout theroad system of Alaska and the Yukon Territory.Implications to surface water storage changeProjecting ecosystem dynamics will moderate concernsand help us plan for a warming Arctic and its effects on35